Purpose is to define the maximum tolerated dose of phenylacetate administered as a 28-day continuous intravenous infusion in children with refractory cancer. Dose-limiting toxicity and incidence and severity of other toxicities of phenylacetate administered will be determined and pharmacokinetics of phenylacetate will be studied. On the first day of therapy, children will receive a 1.8gm/m[2] infusion of phenylacetate over 30 min for determination of pharmacokinetic parameters. This will be followed 24 hours later by phenylacetate, 9gm/m[2]/day (75% of the recommended dose for adult phase II studies), administered as a continuous intravenous infusion for 28 days. Subsequest dose escalations are outlined in detail in the protocol. There will be a 2 week break between each 28 day cycle of therapy. Cycles may be repeated if there is no tumor progression or dose limiting toxicity. The first several days of drug administration should be as an inpatient. If there is no evidence of CNS toxicity or other dose limiting toxicity then the remainder of the cycle and subsequent cycles may be administered on an outpatient basis. Patients will be instructed on the use and care of the portable infusion pump and will return to the clinic daily for medication bag and administration set exchanges. All patients or their legal guardian must give informed consent before starting treatment.